Displacement pumps are known in which one of the displacement wheels disposed in a pump chamber is shiftable and/or translationally movable along its rotational axis and relative to the other of the displacement wheels for adjusting the volume flow. To this end, a piston is disposed on a frontal side of the displacement wheel which is shiftable together with the displacement wheel and forms a sealing gap on a circumferential side together with an enclosure for the piston. On the side of the piston facing away from the displacement wheel, a regulating chamber is disposed in which a means for generating a shifting movement of the piston is disposed.
With this arrangement, the problem often occurs that a pressure fluid present in the pump chamber flows via the sealing gap into the regulating chamber. This leakage of the sealing gap can lead to more or less significant problems in controlling the pump.